Reduced length and low cobalt content cutters and drill bit made therewith

ABSTRACT

A cutter for a fixed cutter drill bit includes a substrate and a cutting material surface affixed to one end of the substrate. The substrate comprises tungsten carbide having at least six percent by weight and at most ten percent by weight of cobalt. An overall length of the cutter is at most 10 millimeters. In one embodiment an overall length of the cutter is at most 8 millimeters.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND

This disclosure is related to the field of fixed cutter drill bits used to drill wellbores through subsurface rock formations. More specifically, the disclosure relates to structures and compositions of cutters used on such drill bits.

Fixed cutter drill bits known in the art include a plurality of cutters affixed to a bit body. The bit body has features to enable coupling to a drill string or other drilling tool that rotates the bit and applies axial force so that the bit drills through rock formations to create a wellbore.

The cutters are typically formed from a substrate in the form of a right cylinder. A diamond “table” made of polycrystalline diamond, or a layer of other “super hard” material, e.g., cubic boron nitride, is affixed to one end of the substrate to for the cutting surface of the cutter.

Cutters of the foregoing type known in the art have about 12 to 15 percent cobalt content in the substrate. An overall length of the cutter is typically about 13 millimeters, including both the substrate and the diamond table or super hard material layer. Shorter cutters are known in the art, however, they generally are only used either in the very center of the bit, called the “cone” (where torsional loading and work rates are a lot lower) or in either backup positions or gage positions. What are known as “primary” cutter positions are positions where the cutters are subjected to the most loading (the positions where the cutters are at the front of the blade and are between the center of the bit and the gage of the bit). Primary cutters may be considered any cutter located radially inwardly of the gage and outwardly of the cone. It is not known in the art to use short cutters (i.e., cutters shorter than about 13 mm overall length) in the above-defined primary cutter locations as it is generally believed that there will not be enough surface area for brazing and that will lead to cutters falling out while drilling.

The cobalt content of cutter substrates known in the art is believed to be necessary to provide the cutters with sufficient resistance to brittle fracture during drilling. The overall length is believed to be necessary to provide sufficient surface area to attach the cutter, typically by brazing the substrate to the bit body, so that the cutters will be attached to the bit body strongly enough to avoid being removed from the bit body during drilling.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a fixed cutter drill bit according to the present disclosure.

FIGS. 2 and 3 show different views of a cutter according to the present disclosure.

DETAILED DESCRIPTION

An example fixed cutter drill bit is shown at 10 in FIG. 1. The bit 10 may include a bit body 12 of any configuration known in the art for fixed cutter bits. The bit body 12 may include one or more blades 13, but such configuration of the bit body 10 is not intended to limit the scope of the present disclosure. The bit body 10 may have attached thereto one or more cutters 14. The cutter(s) will be further explained with reference to FIGS. 2 and 3. As explained in the Background section herein, the so-called “primary” cutters 14 are disposed in an area of the bit face wherein the cutters 14 are subjected to the most loading (the positions where the cutters are at the front of the blade and are between the center or cone of the bit and the gage of the bit). Such cutters may be referred to as “primary cutters.” Other cutters 14A may be disposed proximate an outer edge of the bit body 12, and may be referred to as “gage cutters.” Still other cutter 14B may be disposed on the “cone” section of the bit proximate the axial center of the bit 10. Both the gage cutters 14A and center cutters 14B are subject to much lower loading than the primary cutters 14, and may have different material composition and dimensional requirements than the primary cutters 14. FIG. 2 shows a side view of an example cutter 14 according to the present disclosure. The cutter 14 may include a substantially cylindrical substrate 16 with a cutting material surface 18 affixed to one end of the substrate 16. The substrate 16 and cutting material surface 18 may be substantially cylindrical, but the particular shape of the cutter 14 is not intended to limit the scope of the present disclosure. The cutting material surface 18 may be made from polycrystalline diamond, cubic boron nitride or other “super hard” material known in the art for cutters on fixed cutter drill bits.

In the present example, the substrate 16 may be made from tungsten carbide and have a cobalt content of at most ten percent by weight. In the present example, the substrate 16 may have a cobalt content of at least six percent by weight.

An overall length of the cutter 14 may be about 10 millimeters, including both the substrate 16 and the cutting material surface 18. The thickness of the cutting material surface may be about 2 millimeters in the present example. The substrate is thus about six millimeters in length. In other examples, the overall length of the cutter may be about 8 millimeters, wherein the substrate is about 6 millimeters in length.

An oblique view of the cutter 14 is shown in FIG. 3, wherein the substantially cylindrical shape of the present example cutter 14 is clearly visible.

It has been found through testing that having a cobalt content in the substrate between six and ten percent by weight increases the resistance of the substrate 16 to wear during drilling, but has not resulted in increased incidence of brittle failure. Correspondingly, the overall length of the cutter 14 of about 8 millimeters has been found to provide sufficient bonding surface area to affix the cutter to the bit body (12 in FIG. 1) without cutters becoming removed from the bit body during drilling.

A fixed cutter drill bit made according to the various aspects of the present disclosure may have reduced costs of manufacture, and may have longer usable life span than fixed cutter bits known in the art prior to the bit and cutters of the present disclosure.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims. 

What is claimed is:
 1. A cutter for a fixed cutter drill bit comprising: a substrate; and a cutting material surface affixed to one end of the substrate, wherein the substrate comprises tungsten carbide having at least six percent by weight and at most ten percent by weight of cobalt, and wherein an overall length of the cutter is at most 10 millimeters.
 2. The cutter of claim 1 wherein the cutting material surface comprises at least one of polycrystalline diamond and cubic boron nitride.
 3. The cutter of claim 1 wherein a length of the substrate is about eight millimeters.
 4. The cutter of claim 1 wherein an overall length of the cutter is at most 8 millimeters.
 5. The cutter of claim 4 wherein a length of the substrate is about 6 millimeters.
 6. The cutter of claim 1 wherein the cutter is a primary cutter disposed on a drill bit body radially outside a cone of the bit and radially inside a gage of the bit.
 7. A fixed cutter drill bit comprising: a bit body; and a plurality of cutters affixed to the bit body, each of the cutters comprising a substrate and a cutting material surface affixed to one end of the substrate, wherein the substrate comprises tungsten carbide having at least six percent by weight and at most ten percent by weight of cobalt, and wherein an overall length of each cutter is at most 10 millimeters.
 8. The bit of claim 7 wherein the bit body comprises a plurality of blades.
 9. The bit of claim 7 wherein the cutting material surface of each cutter comprises at least one of polycrystalline diamond and cubic boron nitride.
 10. The bit of claim 7 wherein an overall length of each of the plurality of cutters is at most 10 millimeters.
 11. The bit of claim 10 wherein a length of the substrate of each of the plurality of cutters is about eight millimeters.
 12. The bit of claim 7 wherein an overall length of each of the plurality of cutters is at most 8 millimeters.
 13. The bit of claim 11 wherein a length of the substrate of each cutter is about 6 millimeters.
 14. The bit of claim 7 wherein each of the plurality of cutters is a primary cutter disposed on a drill bit body radially outside a cone of the bit and radially inside a gage of the bit. 